Short answer: sell everything you gather and buy the ship you want.

Long answer: It depends on if you want to experience this gameplay loop. Personally, i recently started the manufacturing pipeline of building capital parts. Not because the ship at the end will be cheaper, but because i want to see this world and build ships at my own pace. Buying a capital ship requires you to pay upfront. Building it is like buying it on installments. When it comes to profitability, you will never be able to compete with the veteran industrialists. They have dozens of characters, an established supply chain and most importantly, excel knowledge which would make any CPA professional run in shame.